In recent history it's mostly the US.

Guess i can't really argue wity that. What remains is the question whether the change was mainly driven by outside forces, or is mainly the result of internal pressure. We know who recently exported the most bigotry, but was it more influencial then the bigotry that was exported there earlier? ¯\_(ツ)_/¯

Obviously this whole chart is outside of the colonial era.

I agree 1993 was after the colonial era, but my point is that Nigeria wasn't a blank slate that was never influenced by anything before they collected the data for this chart.